In the prior art, clear plastic shields, commonly referred to as dust covers, have been proposed for use with combination dial locks. The dust covers are designed to keep fingerprints off the dial and dial ring so that print segments cannot later be re-aligned for discovery of the numbers of the combination. Typically, prior dust covers are annular in shape and are placed over the face of the combination dial for removability. However, prior art dust covers are often removed by authorized users of a combination lock. Once removed, protection against re-alignment and combination discovery through detection of fingerprints on the dial is lost.
It is also known in the field of combination locks to use automatic dialing machines to gain unauthorized access to a security container or secured area. One type of automatic dialing machine engages the grooves in a combination dial knob surface and rotates the combination dial 360.degree. in a succession of predetermined sequences until the correct combination is obtained.
In view of the drawbacks described above for prior art dust covers and the use of automatic dialing machines to gain surreptitious entry, a need has developed to provide improved entry protection devices to effectively limit the use of automatic dialers and fingerprinting of print segments to discover combination number sequences.
In response to this need, the present invention provides an improved entry protection device for combination dial locks which prevents the use of automatic dialing machines and thumb printing of combination dial surfaces to obtain surreptitious entry. The present invention includes indicia features which permit detection of tampering with combination locks, replacement lock or components or unauthorized entry into a combination lock security container or secured area.